In an effort to alleviate handling problems and difficult surface mounting procedures associated with fine-pitch leads of semiconductor devices, some semiconductor manufacturers are building devices in packages which do not employ conventional leads. One such device is the over-molded pad array carrier (OMPAC) device. OMPAC devices have conductive balls, typically solder balls, which are arranged in an array configuration on a bottom surface of a circuitized substrate. The solder balls serve as the external electrical terminals of the device, similar to conventional leads or pins.
One method to manufacture OMPAC devices begins with a semiconductor die mounted to a circuitized substrate. The circuitized substrate typically includes conductive traces on both a top and a bottom surface of the substrate and conductive through-holes or vias which electrically couple the top and bottom traces. The die is electrically coupled to conductive traces on the top surface by, for instance, wire bonds. The die, wire bonds, and a portion of the top surface of the substrate are encapsulated with a resin molding compound. After encapsulation, a solder ball is attached to a terminating end of each of the conductive traces on the bottom surface of the circuitized substrate. The terminating ends of the traces are often formed in the shape of pads and are typically arranged in an array configuration, thus the name "pad array" device.
An existing process for attaching solder balls to the pads on the bottom of a circuitized substrate involves using a vacuum pick-up tool to transfer the solder balls onto the substrate. The pick-up tool picks up a plurality of solder balls such that the balls are arranged in the final array configuration corresponding to the pad configuration on the bottom of the substrate. The pick-up tool then transfers the balls to a flux bath and the balls are partially immersed in the flux. After being coated with flux, the solder balls are transferred to the bottom surface of the substrate such that the balls are aligned with the pads. The solder balls are released from the pick-up tool and reflowed to form a metallurgical bond between each ball and a respective pad.
In practicing the solder ball attachment method described above, a problem of loosing solder balls sometimes occurs during the fluxing procedure. Upon withdrawing the pick-up tool and the solder balls from the flux bath, some solder balls can become dislodged from the tool. If a solder ball is displaced from the pick-up tool, remaining solder balls must be released from the pick-up tool. The pick-up tool then picks up a new set of solder balls and the attachment procedure begins again.
Repeating solder ball attachment operations wastes a significant amount of manufacturing time, thereby increasing costs of OMPAC devices. One solution to the problem of displaced solder balls is to slow the rate at which solder balls are immersed into a flux bath, and also to slow the rate at which the solder balls are withdrawn from the flux bath. While this solution reduces the chance of dislodging a solder ball from the pick-up tool, the slower manufacturing step undesirably increases manufacturing time which in turn increases device cost. Therefore, a less costly and time-consuming solution to the problem of displaced solder balls would be useful.